1. Field of the Application
The invention relates generally to the expression of breast milk. More particularly, the present invention relates to a method of determining a strategic expression regime for mothers who are using a breastpump.
2. Description of the Related Art
Almost all mothers who deliver at term have the physiological capacity to provide milk for their babies. Once lactation is established, the appetite of the baby regulates milk production by local inhibition of milk synthesis independently in each breast as milk accumulates between breastfeedings.
Many mothers who deliver prematurely have a delayed initiation of lactation and are more likely to have a low milk supply. Furthermore, the inability of preterm babies to feed directly from the breasts (for example, due to either sickness or the immature co-ordination of the suck, swallow and breathe reflex) results in their mothers having to use some other means for milk expression, and thereby still provide breast milk for their babies. Thus, these mothers most often use a breastpump for both the initiation and maintenance of their milk supply.
Current expression recommendations particularly for preterm mothers show that increased milk-expression frequency results in an increase in daily milk production. Furthermore, the mechanism controlling the response to expression frequency appears to act locally, at the level of each mammary gland, rather than through a more systemic response. DeCarvalho et al. (1985) was the first to report a strong correlation between daily milk production and frequency of expression, and encouraged preterm mothers to have a frequent milk expression regime that enhanced the likelihood of lactation success. This frequent milk expression regime is now widely practiced. According to this regime, preterm mothers should express frequently (e.g., 6 times per day), and at least 100 minutes per day. In addition, recent studies showed high frequency of breastmilk expression could improve the success of the initiation of lactation, especially for preterm mothers (Hill et al. 2001).
Therefore, there is a general perception that increased expression frequency will result in an increased daily milk production. Obviously, this is a very demanding recommendation for mothers, particularly those who are very concerned about their often fragile, preterm babies. Interestingly, the studies on which these recommendations are based are on milk production per mother, rather than per breast. Consequently, the recommendations do not take into account potential differences between breasts of an individual.
The concept of the autocrine inhibition of milk production, as a result of the accumulation of an inhibitory factor in the milk of a full breast, seems to conveniently explain the observation of increased milk production associated with more frequent breastfeeding and/or breast expression. Furthermore, it has been suggested that the factor acted by a unique mechanism that inhibited the secretion of milk from the Golgi vesicles (Rennison et al. 1993). This enabled a rapid downward regulation of secretion, as milk accumulated in the breast with longer intervals between milk removal. However, Daly et al. (1996) found that the inhibition of milk synthesis in the breast of mothers who delivered at term occurred after intervals of more than six to eight hours. As this study found with term mothers, the large variation of milk yield from each breast resulted in difficulties in assessing the impact of the expression regime on the milk production. Expressing the volume per expression as a proportion of 24 hour milk production (actual milk yield) standardized the difference in the milk yield between breasts, and allowed the analysis of a relationship between proportional milk yield and interval since previous expression. Furthermore, by expressing the 24 hour milk production as 100%, the cumulative expected milk yield (expected milk yield) curve could be calculated essentially for all times from 0 to 24 hours, assuming that the rate of milk synthesis over the day was constant.
Clinically, the goal for pre-term mothers for their total daily milk production has been set in the range of about 350 g/24 hr (Meier et al., personal communication) and 500 ml/24 hr (Hill et al. 2005). There are, however, no consistent guidelines for the volume of milk that these mothers either can or should produce per day. For instance, the minimum daily milk production that mothers should aim for is the minimum volume of milk required for an exclusively breastfed babies at 1-6 months, which is considered to be about 440 ml/24 hr (Kent et al., 2006).
Current expression regimes can place a great demand on mothers who for many reasons do not have the ability to basically be “on-call” to breastfeed a baby; this is especially true for preterm mothers, who are already in a time of extreme stress. Hence, a method that can optimize milk production and minimize the effort for the mothers would greatly enhance their chance of having successful lactation. Further, although the short-term control of milk synthesis occurs at the level of the individual breasts, as a practical matter, expression regimes for mothers need to be similar for both their breasts.